1. Field of the Invention
The present invention relates to control of lead contamination in drinking water supplies, and more particularly, to cathodic protection of lead-containing piping and fixtures from corrosion.
2. Description of the Related Art
For thousands of years, lead has been used to fabricate piping for residential water supplies. Lead is useful for this purpose mainly because of its wide availability, and the relative ease of molding lead into pipes and junctions having desired shapes and sizes.
Because of these characteristics, lead was commonly used in water piping as recently as 1956 in Japan and even into the mid 1960's in Europe. The use of lead-containing piping was particularly common in "service lateral" pipes that connect residences to larger municipal water mains. Even today, lead faucets and fixtures advertised in the United States as being "lead free" can actually contain as much as 8% lead.
The human health hazard posed by lead ingestion is now widely recognized. Lead is a poisonous substance. Intake of even small amounts of lead on a regular basis can cause headaches, dizziness, and insomnia. Ingestion of acute doses of lead can cause stupor, which progresses to coma and then death. There is general agreement among the scientific community that the desirable concentration of lead in drinking water is zero, and the U.S. E.P.A. standard is 15 parts per billion (ppb). The World Health Organization (WHO) Drinking Water Directive (DRD) for lead is 10 ppb.
Recognition of the dangers posed by lead in drinking water supplies has led water authorities in the United States to replace lead-containing piping with substitutes formed from plastic or copper metals. However, domestic water supplied by piping containing lead or lead soldering remains in place in many older homes and in locations throughout the world.
The American Water Works Association has estimated that as of 1990, there were 6.4 million lead goose neck service connections and 3.3 million lead service lines in the United States. It is also estimated that there are over 15 million lead service lines remaining in Europe. It has been estimated that removal and replacement of lead service laterals in Europe will cost over EU $ 50 billion (US $ 61 billion).
Current technology for the control of lead contamination involves options such as removal and relining of pipes, or performing adjustments in water chemistry such as modification of pH and alkalinity and addition of proprietary chemicals. Unfortunately however, these water chemistry adjustments require diligent control and are not effective when a standard of 10 ppb is required, due to the complex chemistry of lead corrosion and dissolution.
The primary known means for lead solubility control are pH adjustment, remineralization, adjustment of alkalinity and addition of phosphate salts. Existing methods for removal of lead in water have focused upon industrial contamination sources having large water flows that contain relatively high lead concentrations. Methods used to treat such large scale contamination include exposure of the contaminated water to biological and chemical agents, or treatment of the water with specialized electrochemical apparatuses. However, these methods are usually complex, require expensive machinery and are typically feasible only for large scale lead contamination. Moreover, it is not feasible to perform these sophisticated treatments at the point of use, such as is required given that the lead contamination comes from the water distribution system itself.
Therefore, where lead-containing residential water piping is still used for service laterals and/or where lead containing water fixtures are present, there is a need in the art for simple and inexpensive apparatuses and methods that permit lead contamination control of existing water pipe configurations having relatively small water flow volumes and low lead concentrations.